[Cutting-edge research on the metabolism of remnant lipoproteins]

Lipoproteins in the plasma transport lipids to various tissues through the bloodstream. In an analysis based on specific gravity using ultracentrifugation, these can be divided into 4 main fractions: chylomicrons, VLDL, LDL, and HDL. Metabolism of the triglyceride-rich (TG-rich) lipoproteins, chylomicrons and VLDL, begins with the hydrolysis of TGs by lipoprotein lipase (LPL) and proceeds through intermediate metabolites (remnants). Those resulting from the former are referred to as chylomicron remnants, and those from the latter as VLDL remnants. Both types of remnant are enriched in cholesteryl esters and apolipoprotein E (apoE), and, moreover, they are referred to as atherogenic lipoproteins that readily accumulate in the arterial walls. At the research level, the analytical methods for remnants such as electrophoresis, ultracentrifugation, gel filtration, etc., are not necessarily simple. One of the methods used as a clinical laboratory test for the quantification of remnant lipoproteins is the remnant-like particle-cholesterol (RLP-C) assay. The significance of the assay as an evaluation for arteriosclerosis is well recognized internationally. Recently, a new method for measuring remnant lipoprotein cholesterol (RemL-C) has been developed that uses a reagent consisting of enzymes and a surfactant. With this method, measurements simply involve an automated analyzer in the same manner as for the homogeneous assay for HDL-C or LDL-C and have been shown to correlate well with values using conventional RLP-C reagents. Measurements can be made simply without the need for special equipment in a short period of time, about 10 minutes. Furthermore, this means that measurements can be made in this way with higher reproducibility and precision. Nevertheless, where the principles behind the two assays are different, discrepancies in the measured values can be identified in some cases. It is also important to understand the characteristics of both methods when using them. After detailing lipoprotein remnant measurement methods, we point out the significance of lipoprotein remnant measurements under conditions that have been the focus of recent particular attention, such as postprandial hyperlipidemia and metabolic syndrome.